^ and that is a statistic of all devices that connected to playstore in a special timeperiod ("Data collected during a 7-day period ending on April 3, 2017"). So it would look even worse for N if all those older Androids that are still in use but don't connect that often to Playstore would have been counted.
And now only Samsung KNOX N devices have special security treatment of OS ontop of N enhancements (afaik) and even S8 is released with only Nougat 7.0.x and not 7.1.x.